1. Field of the Invention
This invention relates to a base plate for an ink jet recording head used for an ink jet recording apparatus which performs recording by forming droplets of ink by discharging ink and attaching the droplets onto a recording medium such as paper, etc. and to an ink jet recording head by use of said base plate.
2. Related Background Art
The ink jet recording method is a method in which recording is performed by discharging ink (liquid for recording) through an orifice (ink discharge port) provided in a recording head and attaching the ink onto a recording medium such as paper. This method has a number of advantages such that generation of noise is extremely small, and also high speed recording is possible, and yet the use of plain paper is possible, i.e., paper for recording having special constitution is not required, and therefore recording heads of various types of this kind have been developed.
Among them, recording heads of the type which permit ink to be discharged through an orifice by applying heat energy to ink have advantages such as good repsonse to recording signals, easy formation of high density multi-orifice, etc.
A typical constitution of such recording heads of the type utilizing heat energy as an ink discharging energy is shown in FIGS. 1A and 1B. FIG. 1A is a sectional view in the flow passage direction of the recording head, and FIG. 1B is a partial exploded view showing the positional relationship of bonding between the base plate and the ceiling plate.
The recording head of FIGS. 1A and 1B shown as an example has a constitution comprising electricity-heat converters arranged on a base plate 1, and further a protective layer provided on the heat-generating resistors 9 and the electrodes 3 of the electricity-heat convertors to be positioned finally under the flow passages 6 and the liquid chamber 11, and a ceiling plate bonded thereto having flow passages 6 and a liquid chamber 11 formed thereon.
The ink discharging energy in this recording head is imparted by the electricity-heat cnoverters 8 each having a pair of electrodes 3 and a heat-generating resistor 9 positioned between the electrodes. More specifically, when heat is generated from the heat-generating resistor 9 by causing a current between the electrodes 3, the ink in the flow passage 6 in the vicinity of the heat-generating resistor 9 is instantaneously heated to generate bubbles there, and droplets of ink are discharged from the orifice through volume change by instantaneous volume expansion and shrinkage by generation of the bubbles.
The protective layer provided on at least the electricity-heat converters in the recording head with the constitution as described above is provided for the purpose of protecting the electrodes and the heat-generating resistors against the ink in the recording head and preventing current leak between a pair of electrodes. Also, particularly for the purpose of protecting the electricity-heat converters from the shock during generation of the discharging energy, a so called cavitation resistance layer may be further provided in some cases.
As a material constituting such a protective layer, inorganic materials having insulating properties such as metal oxides, etc. and organic materials such as resins, etc. have been used in the prior art, and among them, anodically oxidized coatings obtained by anodic oxidation of metal materials have good insulating properties, and also the equipment necessary for preparation thereof is not so large as compared with the vacuum vapor deposition method, thus having the advantage of high productivity, and therefore they are attracting attention as a material capable of constituting the protective layer for electricity-heat converter.
However, in the recording head of the prior art using the anodically oxidized coating as the protective layer or a part thereof, various problems remain yet for utilizing effectively the anodically oxidized film as the protective layer.
For example, in the recording head described in German Offenlegungsshcrift 3403643, a protective layer of high reliability is obtained by anodic oxidation of the electrode surface, and it is described that an anodically oxidized coating may be also formed on the surface of the heat-generating resistor at the same time. Whereas, when protective layers comprising anodically oxidized coating are formed on both of the electrode surface and the heat-generating resistor surface, if the materials of the electrode and the heat-generating resistor are different, the anodically oxidized coatings formed on these surfaces will be different in the characteristics such as composition and volume expansion, and therefore sometimes the protective performance was not sufficient or defects such as cracks are liable to be formed at the boundary portion of the anodically oxidized coating between the electrodes and the heat-generating resistor. Moreover, selection of the conditions and the materials for obtaining good protective performances of anodically oxidized coatings for both the electrode surfaces and the heat-generating resistor surface are greatly limited as compared with the case of forming a single anodically oxidized coating, whereby there is also involved the difficulty that the constituent materials of the recording head such as electrodes, heat-generating resistor, etc. and the conditions of the anodic oxidation cannot be freely selected.
On the other hand, German Offenlegungsschrift 3502900 discloses an ink jet recording head having an inorganic insulating film as the protective layer formed according to the thin film forming technique such as the CVD method, and its defective portions subjected to the anodic oxidation treatment to have anodically oxidized coatings on the electrodes and the heat-generating resistor surfaces existing in the defective portions. Whereas, even if the protective performances of the inorganic insulating film and the anodically oxidized film additionally provided may be good, the protective performance at the boundary therebetween may not be sometimes necessarily sufficient, thus posing a problem to be improved. Also, in this recording head, an inorganic insulating film is formed according to the thin film forming technique, but the thin film forming technique requires a large scale apparatus and also its operations are complicated to involve the problem that productivity and workability are inferior as compared with the anodic oxidation steps or photolithographic steps utilizing a photosensitive resion.
Further, in the bubble type ink jet printing device described in U.S. Pat. No. 4,532,530, a protective layer of an oxidized coating obtained by thermal oxidation of the heat-generating resistor surface at a high temperature of 1000.degree. C. is formed on the heat-generating resistor surface, and also an anodically oxidized coating is formed on the electrodes. While this printing device has the advantage of being capable of production by utilizing the IC production technique or its device as such, the device becomes a large scale and also its operations are complicated. Moreover, it is not suited for producing an ink jet recording head of the so called full multi-type with a large area by a simple device and with good workability.
On the other hand, U.S. Pat. No. 4,535,343 also discloses a thermal ink jet printing head having anodically oxidized coatings provided on the heat-generating resistor surface and the electrode surface. However, this head also had the same problems as in the above German Offenlegungsschrift 3502900.